Printed circuits, in particular, are susceptible to interference by radio frequency (rf) emissions and particularly so when they are coupled together either in side-by-side or stacked relationship. In order to screen the components of PCBs from for example radio interference, PCBs are typically mounted, or ‘sandwiched’ between screening layers formed of conductive material which is maintained at ground potential, thereby to form a multilayer or composite PCB unit.
Typical arrangements of two PCB structures, each comprising a plurality of such multilayer PCB units in a stacked arrangement, are shown in FIGS. 1 and 2 of the accompanying drawings which illustrate isometric views of the arrangements.
In FIGS. 1 and 2, the arrangement in each figure comprises four PCB units 1, 2, 3, 4 mounted in a stack and coupled physically and electrically by vias 5 while maintained in spaced relationship by intervening layers of insulating material 6. The vias 5 provide electrical connection between corresponding layers of the PCB units to ensure that electrical communication can be maintained between them and the components thereof, according to the circuit design, thus to ensure that a uniform potential can be maintained where necessary, i.e. ground potential.
However, it has been observed that the use of vias does permit noise and crosstalk between the interconnected layers due to the vias acting as antennae at radio frequencies.
In our co-pending UK patent application no. GB 0326229.2, there is disclosed an interconnect for electrically connecting striplines or multilayer PCBs, which interconnect is formed as a sandwich of dielectric material held between two ground planes with a strip conductor extending through the dielectric and having an input portion and an output portion. The sandwich is formed by two pieces of dielectric material, each piece being backed by a ground plane and the two pieces of dielectric material being brought together in overlapping relationship.
The arrangement disclosed in the aforesaid application addresses to some extent the band-limiting characteristics of plated-through apertures and over-the-edge connections of the then prior art, which affected the performance of the PCB circuits and gave rise to some signal radiation.